1. Field of the Invention
The present invention relates to a projection display apparatus and, more particularly, to a technique for controlling the cooling of a lamp.
2. Description of the Background Art
In recent years, discharge lamps (xenon lamps, metal halide lamps, high-pressure mercury lamps and the like) have been mainly used as lamps for use in projection display apparatuses. This type of discharge lamp has the drawback of being unable to restart after being turned off if the temperature of the lamp is high.
To remedy this, a conventional projection display apparatus must be turned off after a lamp which has a high temperature during operation is cooled by driving a cooling fan for a certain period of time in order to smoothly perform a lamp-on operation when power supply to the lamp is turned off and then turned on. To shorten the cooling time in this case, for example, a projection display apparatus as disclosed, for example, in Japanese Patent Application Laid-Open No. 4-53943 (1992) is constructed to cool a lamp, after power supply to the lamp is turned off, with a power higher than the cooling power used in the lamp-on state.
It is, however, difficult to ensure the lamp cooling time after the use of the projection display apparatus under all conditions. In some cases, the cooling time required immediately after the projection display apparatus is turned off is not ensured, for example, if the projection display apparatus is turned off by an accident such as power failure or the removal of a power cord or if the projection display apparatus must be stow away quickly.
Even in the above-mentioned cases, the lamp turns on smoothly if a sufficient time interval between the turn-off of the lamp and the subsequent turn-on of the lamp of the projection display apparatus allows the lamp to cool down to a restartable temperature at which the lamp can turn on again. However, the lamp fails to turn on again if the temperature of the lamp remains still high because of the short time interval between the turn-off of the lamp and the restart thereof.
An attempt to forcibly apply high-pressure pulses to the lamp to activate the lamp although the lamp is under conditions of being unable to restart might cause failures such as a circuit malfunction due to pulse noise to result in a breakage of the lamp.